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Oct. 25, 2011 (Orlando, Fla.) -- Children who spend more time outdoors may be less likely to suffer from nearsightedness, a study shows.

In nearsightedness, objects in the distance appear blurry and out of focus.

Researchers who pooled the results of eight previously published studies involving more than 10,000 youngsters found that each additional hour spent outdoors during the week decreased the risk of developing nearsightedness (myopia) by 2%.

"This translates to about a 13% reduced chance of developing nearsightedness per extra hour per day of physical activity outdoors," says researcher Anthony Khawaja, MBBS, an ophthalmologist at the University of Cambridge, U.K.

The study also showed that children who were nearsighted stayed indoors about four hours more per week than children who had normal vision or were farsighted, in which nearby objects appear blurry.

"Increasing children's outdoor time could be a simple and cost-effective measure with important benefits for their vision and general health," Khawaja says. "If we want to make clear recommendations, however, we'll need more precise data."

He presented the findings here at the annual meeting of the American Academy of Ophthalmology (AAO).

Explaining the Role of Outdoor Activity

The researchers were unable to determine the impact of any specific activity on reducing the risk of nearsightedness.

"Is it the physical activity itself? Is it because of exposure to ultraviolet light outside? Is it because they’re spending less time doing close reading? Or is it something else altogether," Sumers asks.

Khawaja agrees. Most of the studies took into account some potential risk factors that could affect the results -- usually age, family history of nearsightedness, and some measure of close activities like reading -- but not all, he says.

The timing of the rise in nearsightedness coincides with the explosion in computer and cell phone use, Khawaja says. At the same time, kids are less likely to engage in the outdoor games of their parents' youth, such as touch football, jump rope, or capture the flag.

Making any definite links requires further study, he says.

One study from China, not included in the current analysis, involved 80 nearsighted children between the ages of 7 and 11, Khawaja says. Half agreed to spend less than 30 hours on close-up work and more than 14 hours outdoors per week.

After two years, children who spent more time outdoors and less time indoors were less likely be nearsighted.

Nearsightedness is much more common in the U.S. and other countries than 40 years ago, according to the American Academy of Ophthalmology. Another study presented at the meeting showed about 4% of preschoolers had nearsightedness.

In some Asian countries, more than 80% of the population is nearsighted.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.